Featured Research

New evidence indicates that the loss of two types of brain cells -- not just one as previously thought -- may trigger the onset of symptoms associated with Parkinson's disease. The evidence, based on mouse models, shows a link between the loss of both norepinephrine and dopamine neurons and the delayed onset of symptoms associated with Parkinson's disease. It was originally thought that the loss of only dopamine neurons triggered symptoms. Dopamine is a neurotransmitter critical for coordinating movement.

Related Articles

The evidence, based on mouse models, shows a link between the loss of both norepinephrine and dopamine neurons and the delayed onset of symptoms associated with Parkinson's disease. It was originally thought that the loss of only dopamine neurons triggered symptoms. Dopamine is a neurotransmitter critical for coordinating movement.

The research was conducted by Karen Rommelfanger, graduate student in the laboratory of David Weinshenker, PhD, assistant professor of human genetics in Emory University School of Medicine and Gary Miller, PhD, associate professor in Emory's Rollins School of Public Health. The team also included Gaylen Edwards and Kimberly Freeman at the University of Georgia.

Parkinson's disease affects motor coordination and is characterized by symptoms such as tremors of hands, arms, legs, jaw and face; rigidity or stiffness of limbs and trunk; bradykinesia, or slowness of movement; and postural instability. The disease most often occurs in those over 50.

"People don't start showing symptoms of Parkinson's disease until about 80 percent of their dopamine neurons are gone, which is when you cross some sort of threshold. Our study looked at what happens while the dopamine neurons are dying and people still appear fine, says Dr. Weinshenker. "The lack of symptoms until the death of most of the dopamine neurons suggested the existence of a system that can temporarily compensate for the loss of the dopamine."

"The dogma in the field is that Parkinson's disease involves a selective loss of dopamine neurons. The truth is, if you look at postmortem Parkinson's disease brains, you will see that both dopamine and norepinephrine neurons are gone," Dr. Weinshenker explains. "We know that norepinephrine is important for regulating the activity of dopamine neurons, so we suspected that the dopamine neurons and the norepinephrine neurons function in concert. As the dopamine neurons start dying, the norepinephrine neurons compensate by signaling the surviving dopamine cells to dramatically increase their activity and the output of dopamine. Eventually, the norepineprhine neurons die, the surviving dopamine neurons lose their ability to release extra dopamine, and symptoms start to appear."

To test their hypothesis, the researchers gave healthy, one-year-old mice the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetra-hydropyridine (MPTP) at a dose that kills about 80 percent of the dopamine cells, but observed no motor impairments in the mice. Surprisingly, when they tested mice unable to synthesize norepinephrine and that have trouble releasing dopamine properly, they observed symptoms of Parkinson's disease including resting tremor, hunched posture and deficits in coordinated movement. These results indicate that having a normal complement of dopamine neurons is not enough for normal motor function; norepinephrine also needs to be present to ensure proper dopamine release.

"Although there are no cures for Parkinson's disease, some moderately effective treatments are available, but most target the dopamine neurons only and are effective for only a limited amount of time. In light of this study, it's quite possible that simultaneously treating both the dopamine and norepinephrine loss could further ameliorate the symptoms of Parkinson's disease,Ó says Dr. Weinshenker.

Results of the study by Emory scientists, along with the University of Georgia, will appear in the Proceedings of the National Academy of Sciences, Early Edition online during the week of Aug. 13-17 and in the Aug. 21 print edition.

More From ScienceDaily

More Mind & Brain News

Featured Research

Mar. 31, 2015 — Memory and as well as connections between brain cells were restored in mice with a model of Alzheimer's given an experimental cancer drug, researchers report. "With this treatment, cells under ... full story

Mar. 31, 2015 — A criminologist finds that solitary confinement does not deter inmates from committing further violence in prison. The prisoners in the study who received solitary confinement were no more -- or less ... full story

Mar. 31, 2015 — Alcoholism takes a toll on every aspect of a person's life, including skin problems. Now, a new research report helps explain why this happens and what might be done to address it. "The clinical ... full story

Mar. 31, 2015 — Human language likely developed quite rapidly into a sophisticated system, a linguist contends. Instead of mumbles and grunts, people deployed syntax and structures resembling the ones we use today, ... full story

Mar. 31, 2015 — Coronary heart disease and stroke, two of the leading causes of death in the United States, are diseases associated with heightened platelet reactivity. A new study in humans suggests an underlying ... full story

Mar. 31, 2015 — A new study had researchers seeking answers to why the therapeutic benefit afforded by SSRIs was so limited in children and teenagers. If researchers can uncover the biological mechanisms preventing ... full story

Mar. 31, 2015 — During prenatal development, the brains of most animals, including humans, develop specifically male or female characteristics. But scientists have known little about the details of how this ... full story

Mar. 31, 2015 — A history of depression may put women at risk for developing diabetes during pregnancy, according to research. This study also pointed to how common depression is during pregnancy and the need for ... full story

Mar. 31, 2015 — Women who are abused by their partner or ex-partner are much less likely to use contraception; this exposes them to sexually transmitted diseases and leads to more frequent unintended pregnancies and ... full story

Featured Videos

AAA: Distracted Driving a Serious Teen Problem

AP (Mar. 25, 2015) — While distracted driving is not a new problem for teens, new research from the AAA Foundation for Traffic Safety says it&apos;s much more serious than previously thought. (March 25)
Video provided by AP

Many Don't Know They Have Alzheimer's, But Their Doctors Do

Newsy (Mar. 24, 2015) — According to a new study by the Alzheimer&apos;s Association, more than half of those who have the degenerative brain disease aren&apos;t told by their doctors.
Video provided by Newsy

A Quick 45-Minute Nap Can Improve Your Memory

Newsy (Mar. 23, 2015) — Researchers found those who napped for 45 minutes to an hour before being tested on information recalled it five times better than those who didn&apos;t.
Video provided by Newsy

Related Stories

Dec. 11, 2014 — A mechanism regulating dopamine levels in the brain has been revealed by a study on a mouse model of late onset Parkinson's disease. Using gene expression profiling, a method to measure the ... full story

May 2, 2012 — Scientists have developed a peptide that protects dopamine-producing neurons, freezing neurodegeneration in its tracks in preclinical trials. This peptide could be easily delivered by daily ... full story

ScienceDaily features breaking news and videos about the latest discoveries in health, technology, the environment, and more -- from major news services and leading universities, scientific journals, and research organizations.